Optical communication systems have replaced other communication mediums due to many advantages associated therewith. For example, optical communication systems typically have wide bandwidth and low attenuation, immunity to electrical noise, and the ability to securely transmit signals over long distances. However, despite the low attenuation that optical communication systems may offer, the optical signals transmitted therein nevertheless require amplification. Although many optical amplifiers currently exist, the most widely used amplifiers are lumped or discrete amplifiers that typically include an optical fiber doped with an optically active material (e.g., Erbium or other rare earth elements). Generally, the core region within the optical fiber contains the dopant, which is optically excited to provide optical gain to an optical signal (e.g., an optical pump signal) having a suitable wavelength. For example, an Erbium-doped fiber amplifier amplifies optical signals that typically have wavelengths in a range between 1520 nanometers (nm) to 1580 nm when pumped by an optical pump signal having a 980 nm or 1480 nm wavelength. Other optical amplifiers that are widely used in optical systems include distributed amplifiers, which typically amplify a signal over a relatively long distributed fiber segment (e.g., a 20 kilometer fiber segment). For example, distributed amplifiers may be based on stimulated Raman scattering or stimulated Brillouin scattering (SBS).
In general, SBS refers to a third-order non-linear optical effect that occurs when an intense beam travelling in a medium (e.g., laser light travelling in an optical fiber) may undergo scattering in a reverse direction from the incoming beam due to variations in the electric field associated with the beam that may produce acoustic vibrations in the medium via electrostriction. The SBS effect tends to be a common phenomenon with a narrow linewidth distributed feedback (DFB) laser. Furthermore, Raman pumps that have many longitudinal modes often exhibit the SBS effect at low power due to modal instability. For Raman amplifiers, the SBS effect tends to be undesirable because the scattering that occurs may change the frequency, path, or other characteristics associated with the beam. Furthermore, when the SBS effect occurs, which has been observed at Raman pump power levels as high as 140 milliwatts (mW), light scattered in the reverse direction from the Raman pump may generate noise propagating in the same direction with the signal in systems that use counter Raman pump schemes.
Raman amplifiers currently tend to rely on a back reflection monitoring circuit to detect back reflection that may require a safety shut down to prevent irreparable damage, hazardous conditions or health risks due to pumping light potentially escaping the optical system, and comply with governmental safety standards. However, because the SBS effect usually exists at lower powers and has a narrow linewidth, the reflection tends to be very high (even higher than at normal reflection at higher Raman power levels), which may force the Raman amplifier to increase a back reflection threshold to avoid possible false Raman safety shutdowns. For example, at one extreme, the SBS effect may cause back reflections that are still above the relevant threshold, which may result in a false Raman pump safety shut down, while at the other extreme, increasing the threshold to prevent a false safety shut down could pose a health risk because imperfect conditions may not be detected and violate applicable laser safety ratings (e.g., standards that define conditions under which a Hazard Level 1M laser may be considered safe). Although pump dithering could potentially be used to broaden the laser linewidth in order to suppress the SBS effect, pump dithering typically will not completely eliminate the SBS effect, and moreover, suitably monitoring SBS events in the optical system may still be desirable even if the SBS effect can be substantially suppressed because the SBS effect can result in scattered light having a substantial impact on gain, noise, bit error rate (BER) hits, and other factors that relate to system performance.